Current tube inspection technology utilizing ultrasonic technology consists of units of three distinct types: 1) rotating head, 2) tube rotates in place, head traverses the length of the tube, and 3) helical advance—canted roller scheme. All three of these methods are restricted by certain constants inherent to the use of ultrasound as a testing medium on all types of products, equipment, and structures.
Few industries require ultrasonic inspection at higher speeds, with greater accuracy than in the inspection of oilfield tubulars such as tubing, casing, and drill pipe. The required speeds and the constant quest to increase the speeds are driven by competitive pressure, steel mill production rates, and the desire to lower manufacturing costs which in turn increase profits.
An article titled “Ultrasonic Testing of Tube—Phased Array Technique” co-sponsored by NDT Systems of France and Sandvik Steel AB of Sweden, goes into extensive detail regarding the inherent problems and shortcomings of current tube testing technology as well as the merits of encircling a tubular product with ultrasonic probes. The co-authors have identified the fairly new technology of phased array ultrasound as the best, cost effective approach to accomplish full body ultrasonic inspection without the use of rotating ultrasonic probes.
In fact, commercially available, non-rotating, phased array tube testing systems are currently operating in production environments at pipe manufacturing facilities. Phased array technology is widely viewed by the next technological leap in the tube testing industry.
It is important to note that the aforementioned reference, published in 1996, has a defined set of “application fields,” but it can be seen that the focus for the end use of the proposed development is the nuclear field, where pipe diameters requiring critical NDT inspections tend to be much smaller than of the most commonly inspected products in the Oil Country Tubular Goods (OCTG) field, which commonly exceed 40 feet in length and whose diameters range from 2 ⅜″ through 20″ and beyond. The reference comments on the known competition in 1996, in which “everybody is working according to conventional technologies: this means single element probes, rotating mechanically around the tube with very complex and expensive systems.” The reference also comments on a specific company called “Nukem.” This company is known to specialize in the inspection of smaller diameter tubes at high speeds. Indeed, it can be reasoned that future development is focused on using the costly phased array method to ultrasonically inspect tubular products.
In addition to the rotating probe approach, also outlined herein are the helical advance conveyor system, the overhead gantry approach, and now the introduction of phased array transducers encircling the pipe as commonly known and accepted approaches to OCTG inspection. It should be noted that these mechanical or technological approaches to ultrasonic tube inspection apply not only to the oil industry, but wherever a cylindrical object may be considered for ultrasonic NDT.
What is unique to the ultrasonic inspection of OCTG is the large surface area needing inspection, coupled with the need for high production rates, which in turn require greater and greater numbers of ultrasonic channels to achieve these goals. The article “Ultrasonic Testing of Tube—Phased Array Technique” describes an electronics data management system to handle between 1000 and 2000 individual ultrasonic transducers.
Currently marketed phased array inspection systems for OCTG, require far more than the contemplated one to two thousand channels, if the systems are to comply with American Petroleum Institute (API) or end user customer specifications for casing and tubing inspection, that require at a minimum, inspection for longitudinal, transverse, and wall thickness abnormalities or flaws. In fact, phased array transducers, covering less than two inches of longitudinal or transverse surface area, can contain up to 256 individual elements and individual channels.
To achieve axial inspection of tubulars without rotation of the tube or test transducers, by definition, the ultrasonic probes must encircle the pipe as contemplated and in use in current phased array systems. Also for minimum inspection requirements acceptable on OCTG, that inspection coverage may require wall thickness measurement as well as transverse and longitudinal flaw inspection. Furthermore, the inspection for longitudinal and transversely oriented flaws, using ultrasonic shear waves, should be conducted from both the leading and trailing sides of a transversely oriented flaw and the counter and counter-clockwise sides of a longitudinal flaw.
Many advances in OCTG ultrasonic inspection have taken place since the first commercialization of the technology in the mid seventies. Now computer controlled digital electronics components allow for higher pulse repetition rates, greater numbers of channels, and wide latitude in the collection and dissemination of the resultant data. Further advances have been made in the manufacture of ultrasonic transducers with the most common types being made of quartz or ceramic materials as outlined and identified in U.S. Pat. No. 4,404,853 to Livingston.
More recently, much research has been done with piezocomposite materials for the manufacture of ultrasonic transducers. In the July 1996 Article “Piezocomposite Transducers—A Milestone for Ultrasonic Testing” by Dr. Gerald Splitt, numerous advantages realized through the use of composite transducers are discussed, including lower signal to noise ratio, high acoustic efficiency, low acoustic impedance, and lower amplifier gain among others. This article is. incorporated by reference herein for all purposes. Of greater importance to the present invention has to do with the method of manufacturing composite sheets that are in turn finished to final transducer element characteristics. Notably, this method described makes it possible to fabricate piezocomposite plates with dimensions of 50×50 mm square or bigger, which are used to produce multiple transducers of smaller size by known methods as mechanical or laser cutting or dicing. Also of note is that piezocomposite can be bent into a cylindrical or spherical shape. This allows one to build line or point focus transducers without the need for an additional lens in front of a crystal. The reference further comments that for arrays and paintbrush probes the construction with piezocomposite transducers becomes substantially easier as here only a light backing is needed to produce high resolution probes.
Those familiar with automated ultrasonic testing will recognize the terms line focus, point focus, arrays, and paintbrush probes as they relate to ultrasonic transducers, and will further recognize the difference between these commonly known probe types and the curved piezocomposite probes outlined and used in the proposed invention.
An additional technical paper of note is “First Results Of Composite Transducers Used in Automatic Rotating Ultrasonic Inspection Units,” authored by Dr Roman Koch and presented in June 2002. This paper goes into much detail regarding actual field testing of composite transducers in automated tube testing machines, specifically the rotating probe method mentioned previously. The article speaks to the aforementioned advantages of piezocomposite probes over conventional transducer elements but is of importance in this case as it relates directly to tube testing. The development of piezocomposite materials for ultrasonic transducers in the middle of the nineties first for the medical probes and then for the standard contact probes gave us the change also to optimize the probes of automatic ultrasonic testing machines to improve the defect sensitivity and resolution. This statement confirms the history of composite probes as well as their short period of use in industrial tube testing applications. The paper goes on to explain in detail the optimization of the sound field and reduction of the lens losses when curving the composite material itself. Again, as in previously referenced articles, the curving addressed is for the sole purpose of focusing the sound beam by curving the composite material in order to improve on inherent shortcomings of using a lens to perform the focusing function. Also of note is the statement that in automated ultrasonic testing systems that in such units often array probes are used where the crystal of the probe is divided in several individual elements, which are connected to individual electronic evaluation channels, to increase testing speed. The use of transducers in combination to increase coverage and speed will be discussed later in detail to point out the advantages of the present inventions improvement over current techniques as well as to draw attention to the uniqueness of the present invention.